w,h,n,R = map(int,input().split())

def dist(x1,y1,x2,y2):
    return ((x1-x2)**2+(y1-y2)**2)**0.5

flag = [[0]*(h+1) for _ in range(w+1)] # flag[i][j]表示是否有记录过
cnt = 0
for k in range(n):
    x,y = map(int,input().split())
    for i in range(x-R,x+R+1):
        for j in range(y-R,y+R+1):
            if 0<=i<=w and 0<=j<=h and flag[i][j]==0 and dist(i,j,x,y) <= R:
                flag[i][j] = 1 # 标记代表已经记录过被覆盖了
                cnt += 1

print(cnt)